The present invention relates to a sheet carrying device for an image forming apparatus, which stably carries a recording medium without causing image blur in a copier, a printer or the like.
In an image forming apparatus such as a copier or a printer, when image formation is performed by using a thick paper having a large weighing capacity, image blur is liable to occur. In general, when the trailing edge of a thick paper passes through a registration roller pair, it is flipped by the registration rollers and the thick paper is instantaneously accelerated. As a result, the thick paper deforms, for example, a transfer belt by its firmness, and the image blur is caused. This is caused because, when the trailing edge of the thick paper passes through the registration rollers, the registration roller pair abruptly returns to the contact state.
Thus, hitherto, a delay mechanism is provided in the registration roller pair, and when the trailing edge of the thick paper passes through, the return of the registration roller pair to the contact state is delayed. This adjustment mechanism is such that a cam is axially attached to one of the registration rollers, and the cam is made to intervene between the shafts of the registration roller pair. By the operation of this cam, when the trailing edge of the sheet passes through, the return of the registration roller pair to the contact state is delayed. That is, after the trailing edge of the sheet passes through the cam, the cam is rotated together with the shaft of the other registration roller, and the registration roller pair slowly returns to the contact state. By this, it is suppressed that the thick paper is accelerated, and the image blur at the time of image formation is prevented.
However, in the conventional adjustment mechanism, even at the time of image formation on a standard paper, the shaft of the registration roller for rotating the cam together is always in contact with a specific position of the cam. Accordingly, the specific position of the cam made of, for example, POM (polyacetal) is worn away by the shaft made of, for example, metal. When the specific portion of the cam is worn away as stated above, the original operation of the cam cannot be obtained, and the cam cannot smoothly rotate during the passage of the thick paper, and besides, after the thick paper passes through, it becomes impossible to smoothly return the registration roller pair to the contact state. Thus, there is a fear that the exchange frequency of the cam increases, and the maintenance property is degraded.
Then, it is desired to develop a sheet carrying device for an image forming apparatus, which prevents a cam of an adjustment mechanism from being worn away, prolongs the life of the cam, and is excellent in maintenance property.